Determining those patients with Cushing's disease who are cured after pituitary microsurgery from those who are incompletely cured has traditionally required prolonged postoperative follow-up. Perioperative changes in plasma ACTH and cortisol concentrations, along with ACTH and cortisol responses to ovine CRH may help delineate sooner those patients in whom surgery was successful as opposed to those patients in whom further intervention is needed.